CN115198328A - Method for electrochemically grafting low-dielectric-constant organic insulating layer on surface of metal interconnection line - Google Patents

Method for electrochemically grafting low-dielectric-constant organic insulating layer on surface of metal interconnection line Download PDF

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CN115198328A
CN115198328A CN202210814846.3A CN202210814846A CN115198328A CN 115198328 A CN115198328 A CN 115198328A CN 202210814846 A CN202210814846 A CN 202210814846A CN 115198328 A CN115198328 A CN 115198328A
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insulating layer
organic insulating
grafting
metal
low
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黄依琴
曹亮
陈丽萍
李明
杭弢
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Shanghai Jiaotong University
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    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
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    • H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
    • H01L21/76801—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the dielectrics, e.g. smoothing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
    • H01L21/76838—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the conductors

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Abstract

The invention discloses a method for electrochemically grafting a low-dielectric-constant organic insulating layer on the surface of a metal interconnection line, namely electrochemically grafting a low-k organic insulating layer on the surface of the metal interconnection line by adopting a diazonium salt reduction technology in an atmospheric atmosphere. The insulation layer grafted by the method is an organic polymer of diazonium salt and monomer, has uniform and controllable thickness and low dielectric constant, can prevent the metal surface from being oxidized, and can be used as a low-k interlayer insulation layer so as to slow down RC delay between interconnection layers. The method can be completely carried out in the atmosphere and at room temperature, and does not need additional inert gas for protection; any soluble monomer containing unsaturated bonds such as double bonds or triple bonds can be grafted; the method has the advantages of wide application range, high reaction speed, simple device, low cost and the like, and is suitable for manufacturing and producing integrated circuits.

Description

Method for electrochemically grafting low-dielectric-constant organic insulating layer on surface of metal interconnection line
Technical Field
The invention belongs to the technical field of materials, and relates to a method for electrochemically grafting a low-dielectric-constant organic insulating layer on the surface of a metal interconnection line, in particular to a method for forming a low-k metal interlayer dielectric layer.
Background
Metal interconnect interlevel dielectric layers are generally classified into two broad categories, inorganic and organic insulating layers. The most commonly used inorganic insulating layer is SiO 2 The dielectric constant is about 3.2-3.8, and the dielectric material can be prepared by thermal growth oxidation, plasma Enhanced Chemical Vapor Deposition (PECVD), physical vapor deposition and other methods, and the process is complicated. And the organic insulating layer has much SiO 2 The dielectric layer has incomparable advantages, and most probably replaces SiO in recent years 2 As a material for the interlayer dielectric layer. They have a low dielectric constant (typically 2 to 3); a lower modulus of elasticity; compared with the preparation method of the silicon dioxide insulating layer, the preparation method of the organic insulating layer is simpler and has lower cost, and the method mainly comprises a spin-coating method, an electrochemical grafting method, a self-assembled monolayer, plasma deposition, chemical grafting and the like. The insulating layer prepared by the spin coating method and the plasma deposition method is in physical contact with the surface of the substrate, so that the interface thermal resistance is increased; the self-assembled monolayer is incapable of forming multiple layers of polymer on the substrate surface; the chemical grafting method mainly comprises two-step chemical grafting based on surface initiated polymerization reaction and one-step grafting based on diazonium salt spontaneous reduction characteristic, wherein the former method needs two steps to complete and has complex process, and the latter method requires a metal substrate to have stronger reducibility and slow reaction speed. The electrochemical grafting method based on the diazonium salt reduction technology has the advantages of high reaction speed, controllable and uniform thickness, capability of obtaining the insulating layer which is covalently connected with the substrate, simple equipment and no strict requirement on environmental conditions, and is an ideal preparation method.
With the continuous development of moore's law, the feature size of ultra large scale integrated circuit (ULSI) devices continues to be miniaturized, and the RC delay caused by interconnection is more significant, which can seriously affect the normal transmission of signals, so that the development of a dielectric material with a low dielectric constant is urgently needed. The dielectric constant of the insulating layer is typically reduced from two aspects: one is to use molecules containing non-polarizable groups such as C-H, C-C, C-Si, C-O and C-F bonds to reduce polarizability; another is to increase the free volume or to introduce controllable nanopores into the membrane, thereby reducing the density of the membrane. For a low-k material with a group which is not easy to polarize, the k value of the PTEE film is the lowest (k = 2.0) under a wide frequency range, but defects of poor processability, surface inertness and the like prevent the PTEE film from being further applied. Although porous membranes can greatly reduce k-value (k = 1.6), it is a challenge how to precisely control the size and distribution of pores. In addition, the generation and distribution of pores is uncontrolled, which often results in insulating layers that are prone to moisture absorption and reduced dielectric properties.
Polyhedral oligomeric silsesquioxane (POSS) belongs to a nanoscale organic-inorganic hybrid material, comprises a cage structure taking inorganic Si-O-Si as a framework, and is applied to preparation of nanoscale composite materials with various potential applications. The POSS is polymerized into the polymer, so that the material has excellent thermal stability, chemical stability and other properties. Meanwhile, the cage structure of POSS can increase the free volume to reduce the density of the insulating layer, thereby reducing the dielectric constant. Thus, POSS-containing polymers are promising candidates for low-k dielectric layers.
The subject group has proposed a method for covalently grafting a dielectric film onto a semiconductor surface by two-step grafting based on the diazonium salt reduction technique. On the basis, the low-k dielectric film can be extended to the metal surface, and can be obtained by only one-step electrochemical grafting, so that the low-k dielectric film is expected to be used as an interlayer dielectric layer between multilevel interconnection metals. Since covalent grafting of the semiconductor surface relies on reduction of the diazo salt with electrons released during the formation of Si-H bonds, but HF destroys the silsesquioxane valence bond, a two-step grafting process is required, i.e., a chemical grafting process is used to form a passivation layer on the semiconductor surface and then electrochemical grafting is performed in a fluorine-free solution to form a low-k organic insulating layer. The metal is more reducing than the semiconductor and does not require prior treatment with HF, so the silsesquioxane is not destroyed. Therefore, the electrochemical grafting can be directly carried out in one step.
Disclosure of Invention
The invention provides a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line, which can be carried out in an atmospheric environment without additional inert gas for protection. And the reaction temperature is lower, and the reaction can be directly carried out at room temperature.
The invention is realized by the following technical scheme:
a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnecting wire, comprising the following steps of:
I. and (3) after cleaning the surface of the metal substrate, immersing the metal substrate into a dilute acid solution to remove an oxide layer on the surface of the metal.
And II, taking the metal as a cathode, taking an inert electrode as an anode, providing voltage by a pulse power supply, immediately putting the metal treated in the step I into a chemical solution mixed with the unsaturated monomer and the aryl diazonium salt for electrochemical grafting reaction, and obtaining the organic insulating layer covalently grafted on the surface of the metal.
The step I of cleaning the surface of the metal substrate specifically comprises the following steps: ultrasonically cleaning the metal matrix in an organic solvent for 5-30min at 10-40 ℃, then putting the metal matrix into a dilute acid solution for cleaning for 30s-5min, and then washing away the acid liquor substances remained on the surface by using ultrapure water or deionized water.
The unsaturated monomer in the step II is a monomer containing double bonds or triple bonds.
The electrochemical grafting method in the step II comprises the following steps: maximum negative pressure V of pulse power supply output waveform on = 5.0 to 11.0V, duration t on =5-30ms; minimum negative pressure V off = 0-2.0V, duration t off ＝60-100ms。
The chemical solution composition in step II comprises: a mixed solvent with the volume ratio of tetrahydrofuran to water of 3-5, 0.002-0.006mol/L vinyl silsesquioxane monomer, 0.007-0.014mol/L aryl diazonium salt and pH value of less than 2, and stirring for 5-20min until the solution is clear and transparent. If solutions with different volumes are prepared, the addition amount can be adjusted according to the composition ratio of the reagents.
The aryl diazonium salt is any one of 4-styryl phenyl tetrafluoroborate diazonium salt, 4-nitrobenzene tetrafluoroborate diazonium salt (NBD) and 4-hydroxybenzene tetrafluoroborate diazonium salt.
The monomer containing double-bond or triple-bond unsaturated bonds is oligomeric silsesquioxane containing double-bond or triple-bond unsaturated bonds.
The oligomeric silsesquioxane monomers include vinyl silsesquioxane and/or propenyl silsesquioxane.
The organic insulating layer prepared by the method for electrochemically grafting the low-k organic insulating layer on the surface of the metal interconnection line also belongs to the protection scope of the invention.
The application of the organic insulating layer in the fields of integrated circuit manufacturing and metal surface organic coating also belongs to the protection scope of the invention.
The inert electrode can be a Pt sheet.
The purpose of cleaning in the step I is as follows: the surfaces of the purchased copper foil, aluminum foil and the like can adsorb some organic or inorganic pollutants, and meanwhile, the oxides on the surfaces of the copper foil and the aluminum foil can prevent the diazonium salt from electronically interacting with the surfaces of the copper, so that the grafting reaction is not facilitated, and therefore, the thorough physical and chemical cleaning is required before grafting. Also, in order to prevent the introduction of excessive impurity ions, the acid used for acid washing is preferably the same as that in the grafted passivation solution.
As an embodiment of the invention, in the step I, the metal substrate cleaning step specifically comprises the steps of sequentially adopting ethanol and acetone for ultrasonic cleaning for 5-30min at the temperature of 10-40 ℃, then putting into a dilute acid solution for cleaning for 30s-5min, and finally washing away substances such as acid liquor and the like remained on the surface by using ultrapure water/deionized water.
Further, the metal substrate cleaning step specifically comprises the steps of respectively ultrasonically cleaning the copper foil or the aluminum foil for 5-30min by sequentially adopting ethanol and acetone at the temperature of 10-40 ℃, then putting into 20% (wt) of dilute sulfuric acid solution for cleaning for 30s-5min, and finally washing away substances such as acid liquor and the like remained on the surface by using ultrapure water/deionized water.
As an embodiment of the invention, in step II, the maximum negative voltage V of the output waveform of the pulse power supply on = 5.0-11.0V, continuouslyTime t on 5-30ms; minimum negative pressure V off = 0-2.0V, duration t off ＝60-100ms。
Compared with the prior art, the invention has the following advantages:
1. the method can be carried out in the atmospheric environment, and does not need additional inert gas for protection. And the reaction temperature is lower, and the reaction can be directly carried out at room temperature.
2. The electrochemical grafting device is simple, can be put into use by using the existing electroplating equipment or slightly modifying the existing electroplating equipment, and can avoid huge capital investment and equipment depreciation cost.
3. The thickness of the low-k organic insulating layer electrochemically grafted on the metal surface is uniform and controllable, the growth speed is high, and the thickness of the insulating layer film can reach 200nm after grafting for 30s-1 min; the insulating layer is formed by crosslinking a high-temperature-resistant Si-O frame structure, and has good thermal stability and is suitable for the high-temperature treatment process of BEOL; most importantly, the k value of the organic insulating layer grown by the method can be very low (1.75-1.67, 600-1700 nm).
4. The method is also suitable for grafting other soluble monomers containing unsaturated bonds such as double bonds or triple bonds on the metal surface.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of a pulse power waveform applied by electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line according to the invention;
FIG. 2 is a microscopic infrared spectrum of a thin film obtained by electrochemical grafting of octavinyl silsesquioxane (OVS) monomer onto a Cu surface under the conditions of example 1;
FIG. 3 is a graph of dielectric constant as a function of wavelength for films obtained by electrochemically grafting octavinyl silsesquioxane (OVS) monomer onto a Cu surface under the conditions of example 1;
FIG. 4 is an X-ray photoelectron spectrum of a film obtained by electrochemically grafting octavinyl silsesquioxane (OVS) monomer on the surface of Cu under the conditions of example 1;
FIG. 5 is a graph of dielectric constant as a function of wavelength for films formed by electrochemically grafting octavinyl silsesquioxane (OVS) monomer onto a Cu surface under the conditions of example 2 in accordance with the present invention;
FIG. 6 is a digital photographic image of a Cu surface after chemical grafting of octavinyl silsesquioxane (OVS) monomer onto the Cu surface in accordance with the present invention;
FIG. 7 is a microinfrared spectrum of a film of the present invention chemically grafted octavinyl silsesquioxane (OVS) monomer on the Cu surface.
FIG. 8 is a graph showing the change of dielectric constant with wavelength of a film obtained in comparative example 5 by grafting octavinyl silsesquioxane (OVS) monomer onto the Cu surface in two steps;
Detailed Description
The present invention will be described in detail with reference to examples. The following examples will aid those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any manner. It should be noted that numerous modifications and adaptations can be made by those skilled in the art without departing from the inventive concepts herein. All falling within the scope of the present invention.
Example 1
The embodiment relates to a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line.
The metal substrate may be Al or Cu, (Cu is selected as the substrate in this embodiment), and the monomer may be a soluble monomer having an unsaturated bond such as a double bond or a triple bond (octavinyl silsesquioxane (OVS) is selected as the monomer in this embodiment).
The preparation method of the electrochemical grafting low-k organic insulating layer on the surface of the metal interconnection line comprises the following steps:
step I, sequentially and respectively ultrasonically cleaning the Cu sheet for 5min by using ethanol and acetone at the temperature of 25 ℃, then cleaning the Cu sheet for 30s by using 20% dilute sulfuric acid, and finally washing the Cu sheet by using ultrapure water.
Step II, placing the cleaned Cu sheet into a prepared chemical solution for electrochemical grafting reaction at the temperature of 20 ℃, wherein the Cu sheet is used asThe cathode is a Pt plate, the anode is a Pt plate, and the voltage applied by the reaction is provided by a pulse power supply. The waveform diagram of the pulse power supply is shown in FIG. 1, where V on To output the maximum negative pressure of the waveform, take-9.5V for a duration t on Is 20ms, V off The minimum negative pressure of the output waveform is-0.5V, the duration is 90ms, and the electrochemical grafting time is 1min.
Step III, washing the grafted Cu surface by acetonitrile to remove physical adsorbates, thus obtaining the metal surface electrochemical grafted organic insulating layer;
the preparation process of the chemical solution is as follows: 47.5ml of tetrahydrofuran and 0.004mol/L of octavinyl silsesquioxane are added into a Teflon beaker, and after being dissolved for a period of time, 12.5ml of ultrapure water, 1.5ml of concentrated sulfuric acid and 0.01mol/L of 4-nitrophenyl tetrafluoroborate diazonium salt are added and stirred for 20min by a magnetic stirrer until the solution is clear and transparent.
Step IV, measuring the group composition by using microscopic infrared as shown in figure 2, wherein the concentration is 1109.63cm -1 There is a Si-O-Si peak and it can therefore be confirmed that OVS can be grafted to the Cu surface by this method. The dielectric constant k of the organic insulating layer on the surface of Cu was measured to be 1.75-1.67 (wavelength 600-1700 nm) using an ellipsometer, as shown in FIG. 3. The corresponding thickness =200nm was measured with a step meter. The X-ray spectrometer is used to measure the bonding and content of the elements on the surface of the film, and as can be seen from the spectrogram in FIG. 4, the Si-O bond of OVS occupies a certain strength, and the atomic percentages of the elements C, O, N and Si are 70.73%,15.58%,7.57% and 6.13%, respectively.
Example 2
The embodiment relates to a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line.
The metal substrate may be Al or Cu (Cu is selected as the substrate in the present embodiment), and the monomer may be a soluble monomer having an unsaturated bond such as a double bond or a triple bond (octavinyl silsesquioxane (OVS) is selected as the monomer in the present embodiment).
The preparation method of the electrochemical grafting low-k organic insulating layer on the surface of the metal interconnection line comprises the following steps:
step I, ultrasonically cleaning the Cu sheet for 5min by using ethanol and acetone in sequence at the temperature of 25 ℃, then cleaning the Cu sheet for 30s by using 20% dilute sulfuric acid, and finally washing the Cu sheet by using ultrapure water.
And step II, putting the cleaned Cu sheet into a prepared chemical solution at the temperature of 20 ℃ to perform electrochemical grafting reaction, wherein the Cu sheet is used as a cathode, the Pt sheet is used as an anode, and the voltage applied by the reaction is provided by a pulse power supply. The waveform diagram of the pulse power supply is shown in FIG. 1, where V on To output the maximum negative pressure of the waveform, take-7.5V for a duration t on Is 20ms, V off To output the minimum negative pressure of the waveform, take-0.5V, duration t off The electrochemical grafting time was 30min at 90 ms.
Step III, washing the grafted Cu surface by using acetonitrile to remove physical adsorbates, thus obtaining the metal surface electrochemical grafted organic insulating layer;
the preparation process of the chemical solution comprises the following steps: 37.5ml of tetrahydrofuran and 0.003mol/L of octavinyl silsesquioxane are added into a Teflon beaker, and after a period of dissolution, 10ml of ultrapure water, 1.0ml of concentrated sulfuric acid and 0.014mol/L of 4-nitrophenyl tetrafluoroborate diazonium salt are added and stirred for 20min by a magnetic stirrer until the solution is clear and transparent.
And IV, testing the dielectric constant k of the organic insulating layer on the surface of the Cu to be 2.98-2.76 (the wavelength is 600-1700 nm) by using an ellipsometer, as shown in FIG. 5. The corresponding thickness was 2 μm measured with a step meter.
Example 3
The embodiment relates to a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line. The metal substrate may be Al or Cu (Cu is selected as the substrate in the present embodiment), and the monomer may be a soluble monomer having an unsaturated bond such as a double bond or a triple bond (octavinyl silsesquioxane (OVS) is selected as the monomer in the present embodiment).
The preparation method of the electrochemical grafting low-k organic insulating layer on the surface of the metal interconnection line comprises the following steps:
step I, ultrasonically cleaning the Cu sheet for 5min by using ethanol and acetone in sequence at the temperature of 25 ℃, then cleaning the Cu sheet for 30s by using 20% dilute sulfuric acid, and finally washing the Cu sheet by using ultrapure water.
And step II, putting the cleaned Cu sheet into a prepared chemical solution at the temperature of 20 ℃ to perform electrochemical grafting reaction, wherein the Cu sheet is used as a cathode, the Pt sheet is used as an anode, and the voltage applied by the reaction is provided by a pulse power supply. The waveform diagram of the pulse power supply is shown in FIG. 1, where V on To output the maximum negative pressure of the waveform, take-11.0V for a duration t on Is 30ms, V off To output the minimum negative pressure of the waveform, take 0V, duration t off 80ms, electrochemical grafting time is 5min.
Step III, washing the grafted Cu surface by using acetonitrile to remove physical adsorbates, thus obtaining the metal surface electrochemical grafted organic insulating layer;
the preparation process of the chemical solution is as follows: 50.0ml of tetrahydrofuran and 0.006mol/L of octavinyl silsesquioxane are added into a Teflon beaker, and after being dissolved for a period of time, 10.0ml of ultrapure water, 1.5ml of concentrated sulfuric acid and 0.010mol/L of 4-nitrophenyl tetrafluoroborate diazonium salt are added and stirred for 20min by a magnetic stirrer until the solution is clear and transparent.
And IV, testing the dielectric constant k of the organic insulating layer on the Cu surface to be 2.53-2.21 (the wavelength is 600-1700 nm) by using an ellipsometer, and measuring the corresponding thickness to be 500nm by using a step profiler.
Example 4
The embodiment relates to a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line. The metal substrate may be Al or Cu (Cu is selected as the substrate in the present embodiment), and the monomer may be a soluble monomer having an unsaturated bond such as a double bond or a triple bond (octavinyl silsesquioxane (OVS) is selected as the monomer in the present embodiment).
The preparation method of the electrochemical grafting low-k organic insulating layer on the surface of the metal interconnection line comprises the following steps:
step I, ultrasonically cleaning the Cu sheet by using ethanol and acetone for 5min respectively at the temperature of 25 ℃, then cleaning the Cu sheet by using 20 percent dilute sulfuric acid for 30s, and finally washing the Cu sheet by using ultrapure water.
Step II, putting the cleaned Cu sheet into the furnace at the temperature of 20 DEG CAnd carrying out electrochemical grafting reaction in a prepared chemical solution, wherein the Cu sheet is used as a cathode, the Pt sheet is used as an anode, and the voltage applied by the reaction is provided by a pulse power supply. The waveform diagram of the pulse power supply is shown in FIG. 1, where V on To output the maximum negative pressure of the waveform, take-5.0V for a duration t on Is 20ms, V off To output the minimum negative pressure of the waveform, take-2.0V, duration t off 100ms, electrochemical grafting time 20min.
Step III, washing the grafted Cu surface by using acetonitrile to remove physical adsorbates, thus obtaining the metal surface electrochemical grafted organic insulating layer;
the preparation process of the chemical solution comprises the following steps: adding 35ml of tetrahydrofuran and 0.002mol/L of octavinyl silsesquioxane into a Teflon beaker, dissolving for a period of time, adding 10ml of ultrapure water, 1.0ml of concentrated sulfuric acid and 0.008mol/L of 4-nitrophenyl tetrafluoroborate diazonium salt, and stirring for 20min by using a magnetic stirrer until the solution is clear and transparent.
And IV, testing the dielectric constant k of the organic insulating layer on the Cu surface to be 2.01-1.87 (the wavelength is 600-1700 nm) by using an ellipsometer. The corresponding thickness was measured with a step meter to be 50nm.
Example 5
The embodiment relates to a method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line. The metal substrate may be Al or Cu (Al is selected as the substrate in this embodiment), and the monomer may be a soluble monomer having an unsaturated bond such as a double bond or a triple bond (octavinyl silsesquioxane (OVS) is selected as the monomer in this embodiment).
The preparation method of the electrochemical grafting low-k organic insulating layer on the surface of the metal interconnection line comprises the following steps:
step I, ultrasonically cleaning the Al sheet by using ethanol and acetone in sequence for 5min respectively at the temperature of 25 ℃, then cleaning the Al sheet by using 20 percent dilute sulfuric acid for 30s, and finally washing the Al sheet by using ultrapure water.
And step II, putting the cleaned Al sheet into a prepared chemical solution at the temperature of 20 ℃ to perform electrochemical grafting reaction, wherein the Al sheet is used as a cathode, the Pt sheet is used as an anode, and the voltage applied by the reaction is provided by a pulse power supply. The waveform diagram of the pulse power supply is shown in FIG. 1, in which Von is the maximum negative pressure of the output waveform, and is-9.5V, the duration ton is 20ms, voff is the minimum negative pressure of the output waveform, and is-0.5V, the duration is 90ms, and the electrochemical grafting time is 1min.
Step III, washing the grafted Al surface by using acetonitrile to remove physical adsorbates, thus obtaining an organic insulating layer electrochemically grafted on the metal surface;
the preparation process of the chemical solution is as follows: 47.5ml of tetrahydrofuran and 0.004mol/L of octavinyl silsesquioxane are added into a Teflon beaker, and after being dissolved for a period of time, 12.5ml of ultrapure water, 1.5ml of concentrated sulfuric acid and 0.01mol/L of 4-nitrophenyl tetrafluoroborate diazonium salt are added, and the mixture is stirred for 20min by a magnetic stirrer until the solution is clear and transparent.
And IV, measuring the corresponding thickness by using a step profiler to be 80nm. The reducibility of Al is stronger than that of Cu, and under the same experimental conditions, the grafting speed of Al is faster than that of Cu, so that the formed dielectric film is thicker.
Comparative example 1
The specific steps are different from those in example 1 only in that the cleaned copper sheet is directly put into a prepared chemical solution for chemical grafting reaction without external power supply. After 12h of reaction, the Cu surface has no obvious sign of organic film growth, probably because the open circuit potential of Cu in the solution is not much more negative than the reduction potential of diazonium salt, so that spontaneous redox reaction between Cu and diazonium salt is difficult to occur. Thus, the open circuit potential of the solution is very high in this way, which presents another challenge to the solution formulation.
Comparative example 2
The comparison example relates to a method for chemically grafting a dielectric film on the surface of a metal, and the specific steps are different from those of the example 1) that 1) the cleaned copper sheet is directly put into a prepared chemical solution for chemical grafting reaction without external power supply; 2) And adding a small amount of reduced iron powder into the uniformly dissolved chemical solution. After 1h of reaction, the appearance is obviousA very thin film covering the Cu surface was observed as shown in fig. 6. The radical composition is shown in FIG. 7 by microinfrared measurement at 1072.26cm -1 There is a weaker Si-O-Si peak, thus confirming that octavinyl silsesquioxane can be grafted to the Cu surface by this method. Although the addition of reduced iron powder accelerates the progress of the chemical grafting reaction, the reaction period is much longer than that of the electrochemical grafting; meanwhile, iron powder is easily adhered to the film and is difficult to remove and easy to oxidize, which is a great abstain for the electronic industry with high requirements on cleanliness.
Comparative example 3
The present comparative example relates to a method for electrochemically grafting a dielectric film on a metal surface, and the specific steps are different from those of example 1 only in that nitrogen salt is not added during the preparation of a chemical solution, and other conditions are the same. No bubble formation of the solution near the cathode was observed and no visible film coverage of the metal surface was observed even when the grafting time was extended to 1 hour.
Comparative example 4
The comparison example relates to a method for electrochemically grafting a dielectric film on a metal surface, and the specific steps are different from those of the example 1 only in that the monomer selected for preparing the chemical solution is different, the comparison example selects methyl methacrylate, and other conditions are the same. The dielectric constant k of the organic insulating layer on the Cu surface is tested to be 2.71-2.43 (the wavelength is 600-1700 nm) by an ellipsometer, and is higher than that of a dielectric film taking octavinyl silsesquioxane as a monomer. In conclusion, the method of the invention is to electrochemically graft a low-k organic insulating layer on the surface of a metal by adopting a diazonium salt reduction technology in an atmospheric atmosphere. The insulating layer is composed of organic polymers of diazonium salt and octavinyl silsesquioxane, the thickness is uniform and controllable, the thickness can be realized within 50nm-2 mu m, the dielectric constant can be very low (1.75-1.67, 600-1700 nm), and the insulating layer can be used as an inter-metal dielectric layer for slowing down RC delay during multilevel interconnection; and any soluble monomer containing unsaturated bonds such as double bonds or triple bonds can be grafted on the metal surface by the method.
Comparative example 5
The comparative example relates to a method for electrochemically grafting a dielectric film on a metal surface, and the specific steps are different from those of the example 1 only in that: 1) A two-step grafting method was used, i.e. according to the method of the prior patent 202010954601.1, the passivation layer was formed on the metal surface by chemical grafting for 30s in a diazonium salt solution, and then electrochemical grafting was carried out in a chemical solution containing an Octavinylsilsesquioxane (OVS) monomer under the same conditions as in example 1. 2) Multiple formulations of chemical solutions for chemical grafting are required.
The dielectric constant of the dielectric thin film was measured by an ellipsometer to be 1.78-1.70 (600-1700 nm), as shown in FIG. 8, corresponding to the result of example 1, and the film thickness was 100nm. The two-step grafting method is equivalent to one-step electrochemical grafting because HF and Cu basically do not react and can not release electrons, diazo salt cannot undergo a reduction reaction to form free radicals, and the first-step chemical grafting cannot successfully form a passivation layer on the surface of Cu. While the results of comparative example 1 may also demonstrate the challenge of chemical grafting on Cu. If the first step of chemical grafting can be carried out smoothly, the proportion of the passivation layer of the film is increased, which is not beneficial to the reduction of the dielectric constant, the dielectric constant of the dielectric film grafted in the prior patent 202010954601.1 is 2.1-2.2, the film thickness is 50nm, and the total grafting time is 6min. The grafting time was longer, but the dielectric film was thinner and the dielectric constant was higher, compared to example 1. The method of the invention therefore has the following advantages: 1. the process is simplified, and a two-step grafting method is combined into one step of electrochemical grafting; 2. the growth rate of the film is accelerated, and a thicker film can be obtained in a shorter time; 3. the dielectric constant of the dielectric film is lower than that of the two-step grafting method in which the first step is successfully chemically grafted.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (10)

1. A method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line is characterized by comprising the following steps:
I. the surface of the metal substrate is immersed in a dilute acid solution after being cleaned, and an oxide layer on the surface of the metal is removed;
and II, using metal as a cathode and an inert electrode as an anode, providing voltage by a pulse power supply, and immediately putting the metal treated in the step I into a chemical solution mixed with an unsaturated monomer and an aryl diazonium salt for electrochemical grafting reaction to obtain an organic insulating layer covalently grafted on the surface of the metal.
2. The method for electrochemically grafting a low-k organic insulating layer on the surface of a metal interconnection line according to claim 1, wherein the step of cleaning the surface of the metal substrate in the step I specifically comprises the steps of:
ultrasonic cleaning the metal matrix in an organic solvent for 5-30min at 10-40 ℃, then putting the metal matrix into a dilute acid solution for cleaning for 30s-5min, and then washing away the acid liquor substances remained on the surface by using ultrapure water or deionized water.
3. The method for electrochemically grafting a low-k organic insulating layer onto the surface of a metal interconnection line according to claim 1, wherein the unsaturated monomer in step II is a monomer containing a double bond or a triple bond.
4. The method for electrochemically grafting a low-k organic insulating layer onto the surface of a metal interconnection line according to claim 3, wherein the monomer containing double-bond or triple-bond unsaturated bonds is oligomeric silsesquioxane containing double-bond or triple-bond unsaturated bonds.
5. The method of electrochemically grafting a low-k organic insulating layer onto a surface of a metal interconnect line of claim 4, wherein the oligomeric silsesquioxane monomer comprises vinyl silsesquioxane and/or propenyl silsesquioxane.
6. The method for electrochemically grafting a low-k organic insulating layer onto the surface of a metal interconnection line according to claim 1, wherein the electrochemical grafting conditions in step II are as follows: pulse power supply output waveformMaximum negative pressure V of on = 5.0 to 11.0V, duration t on 5-30ms; minimum negative pressure V off = 0-2.0V, duration t off ＝60～100ms。
7. The method for electrochemically grafting a low-k organic insulating layer onto a surface of a metal interconnection line according to claim 1, wherein the chemical solution composition in step II comprises: mixed solvent with volume ratio of tetrahydrofuran to water of 3-5, vinyl silsesquioxane monomer in 0.002-0.006mol/L, aryl diazonium salt in 0.007-0.014mol/L and pH value less than 2, and stirring for 5-20min until the solution is clear and transparent.
8. The method for electrochemically grafting a low-k organic insulating layer onto the surface of a metal interconnection line according to claim 1, wherein the aryl diazonium salt is any one of 4-styryl phenyl tetrafluoroborate diazonium salt, 4-nitrophenyl tetrafluoroborate diazonium salt (NBD) and 4-hydroxyphenyl tetrafluoroborate diazonium salt.
9. The organic insulating layer prepared by the method for electrochemically grafting the low-k organic insulating layer on the surface of the metal interconnection line according to any one of claims 1 to 8.
10. Use of the organic insulating layer according to claim 9 in the field of integrated circuit manufacture, organic coating of metal surfaces.
CN202210814846.3A 2022-07-12 2022-07-12 Method for electrochemically grafting low-dielectric-constant organic insulating layer on surface of metal interconnection line Pending CN115198328A (en)

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